<http://purl.org/dc/terms/description>
"The common industrial practice of using aqueous solutions of diethanolamine (DEA) for the removal of impurities such as carbon dioxide (CO\u2082), hydrogen sulphide (H\u2082S), carbonyl sulphide (COS) and carbon disulphide (CS\u2082) from natural, refinery and manufactured gases often entails irreversible reactions between the solvent and the impurities. This phenomenon is referred to as amine degradation and it not only constitutes a loss of the amine but may contribute to operational problems such as foaming, corrosion and fouling.\r\nDegradation of DEA by COS and CS\u2082 was studied by using a 600 mL stainless steel reactor under the following conditions: DEA concentration 10 - 40 wt%; temperature 120 - 195 \u00B0C; COS partial pressure 345 - 1172 kPa; CS\u2082 volume 2.5 - 10.5 mL (CS\u2082/DEA mole ratio of 0.055 - 0.233). An analytical procedure consisting of gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS) was used to identify over 20 compounds in the partially degraded DEA solutions. The major degradation products are monoethanolamine (MEA), bis hydroxyethyl ethylenediamine (BHEED), bis hydroxyethyl piperazine (BHEP), hydroxyethyl oxazolidone (HEOD), hydroxyethyl imidazolidone (HEI), tris hydroxyethyl ethylenediamine (THEED) and bis hydroxyethyl imidazolidone (BHEI); as well as a dithiocarbamate salt (in the case of the CS\u2082-DEA systems). In addition, both COS and CS\u2082 induced degradation formed solid products which were characterized on the basis of solubility, melting point, elemental composition, solid probe GC/MS and infrared analysis. The number of degradation compounds in the COS-DEA\r\nand CS\u2082-DEA systems is large when compared with the three major degradation compounds found in CO\u2082-DEA systems; this demonstrates that the former systems are distinct and more complicated than the latter system.\r\nWhen COS or CS\u2082 was contacted with aqueous DEA solution, hydrolysis occurred and H\u2082S, CO\u2082, COS and, possibly, CS\u2082 together with their related ionic species were present in the system. Solubility and hydrolysis experiments were therefore conducted to establish the equilibrium composition of the COS-DEA system prior to the commencement of degradation. A modified Kent-Eisenberg (K/E) model which was developed to correlate the experimental data, showed good agreement between the experimental results and model predictions. Since the K/E and previous models were limited to amine-CO\u2082 and/or H\u2082S systems, the present modified K/E model which incorporates COS, is a significant improvement.\r\nThe rate of degradation of DEA was found to increase with temperature, DEA concentration, COS partial pressure and CS\u2082 volume. On the basis of the experiments conducted to evaluate the contributions of the various compounds in the partially degraded solutions, reaction schemes were developed for the formation of 18 degradation compounds in the COS-DEA and CS\u2082-DEA systems. Despite the complexity of the reactions, the overall degradation of DEA was well represented by a first order reaction for the present experimental conditions. A mathematical model based on the major reaction schemes was developed to estimate the concentrations of DEA and the major degradation compounds in the COS-DEA system.\r\nContrary to literature information, experiments conducted with gas mixtures of CO\u2082 and showed that H\u2082S enhanced the rate of DEA\r\ndegradation. A direct result of the combined effects of H\u2082S and CO\u2082 on alkanolamines was the production of the corresponding lower order alkanolamines from higher order ones. The resulting mixed amine solution increases the routes for degradation compared to single amine solutions. The study therefore provides an indication of what to expect in terms of degradation when mixtures of alkanolamines are used for gas sweetening."@en
<https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0059005>